The invention is directed to new sulfur-containing diisocyanates in which a mercapto, sulfoxo or sulfone group joins two aromatic nuclei together or joins an aromatic nucleus to an aliphatic group and in which at least one of the aromatically bound isocyanate groups is in the ortho-position to the sulfur atom. The invention is also directed to a process for the preparation of these new sulfur-containing diisocyanates and to their use in the isocyanate polyaddition process for the production of polyurethanes.
Aromatic diisocyanates in which the aromatic nuclei are joined by sulfur and in which the isocyanate groups are in the p,p'- or m,m'- or o,o'-positions to the sulfur atom are known (JA 74-048196; JA 38985/71). But sulfur-containing diisocyanates in which the aromatically bound isocyanate groups are in the o,p'-positions to the sulfur atom and sulfur-containing isocyanates which have an aromatically bound and an aliphatically bound isocyanate group in which the aromatically bound isocyanate group is in the ortho-position to the sulfur atom have not hitherto been disclosed. These compounds are new, interesting components for the synthesis of polyurethanes. They enable preparation of polyurethane elastomers having excellent mechanical properties. Furthermore, due to the greatly differing reactivities of the isocyanate groups thereof, they may be used for reactions with Zerewitinoff active compounds so as to produce predetermined results.
It is particularly surprising to find that it is not only the aromatic-aliphatic diisocyanates of the invention but also those diisocyanates of the invention in which all the isocyanate groups are aromatically bound that have isocyanate groups which differ considerably in reactivity. Moreover, the isocyanate group which is in the ortho-position to sulfur has an approximately ten times higher reactivity with compounds containing active hydrogen atoms than the isocyanate group which is in the para-position. This difference in the reactivity of the two isocyanate groups is found in the unsubstituted diisocyanates of the invention. However, the difference in reactivity may be enhanced by the presence of electron attracting substituents in the para-position to that isocyanate group which is in the ortho-position to the sulfur atom and/or by the presence, in the ortho-position to that isocyanate group which is in the para-position to the sulfur atom, of a substituent which has a sterically hindering effect on the isocyanate group in the para-position to the sulfur atom.
The diisocyanates of the invention are, therefore, particularly valuable starting materials for the production of polyurethanes. They are suitable for the production of polyurethanes by the prepolymer or one-shot process using highly reactive chain-lengthening agents. Starting materials using the diisocyanates of the invention combine the advantage of a sufficiently long pot life due to the relative inertia of the more slowly reacting isocyanate group with the advantage of a desirably short molding time. Compared to molded products produced from known diisocyanates, such as 4,4'-diisocyanato-diphenylmethane or 2,4'-diisocyanato-diphenylmethane, the polyurethane products obtained using the diisocyanates of the invention may be removed more easily from the mold without damage because they resist breaking much more effectively by bending much more quickly.